Radio receiver circuits are used in many different applications, such as cellular communications. Signals received by a radio receiver circuit may be relatively weak and need to be amplified. Hence, an amplifier is typically included in the radio receiver circuit. Such an amplifier should not add too much noise to the received signal. Therefore, a so called low-noise amplifier (LNA) is often used for this purpose.
Some existing radio communications systems, such as fourth generation (4G) and fifth generation (5G) cellular communications systems, the used signal bandwidth is often relatively large, such as tens or hundreds of MHz. Furthermore, it should be possible to tune a receiver center frequency over a relatively large frequency range. One challenging task in the design of receiver amplifiers, such as LNAs, is to achieve an input impedance matching with enough frequency bandwidth. Such relatively wideband input impedance matching should preferably be obtained while at the same reaching sufficiently high performance in terms of other parameters of the LNA, such as gain and frequency selectivity.